Hi,
Let's consider a few simple and concrete examples.
Mary cooked dinner. She did this at some point in the past. Typically, the speaker would also tell us when.
eg At 8pm last Friday, Mary cooked dinner.
Mary has cooked dinner. Theis tense indicats the statement has importance in the present.
Dinner is on the table! We don't need to be told when exactly she did this.
Mary had cooked dinner. She did this in the past, before some later point in the past. We need to be told what that later point was.
eg Tom came home at 7pm last night. Mary had cooked dinner. It was sitting on the table, so they sat down and ate it.
Perhaps now you would like to review your earlier post. Do you still have questions? If so, please ask them again.
If you search the Forum for 'Present Perfect' and 'Past Perfect', you will find a great deal of discussion about these tenses.
Best wishes, Clive